Strains of Pseudomonas aeruginosa isolated from sediments in wells showed a greater bacteriocinogenic activity in those isolated from river and clinical specimens. More than half of all the strains examined had extrachromosomal DNA. Plasmid DNA was extracted from all the strains and in only 24/120, all from different origins, was the curing achieved; all these strains coded their bacteriocins in the chromosomal DNA